1. Field
Embodiments of the present invention relate to a decelerator which restricts an increase in the axial thickness of a motor and achieves an effectively increased deceleration ratio, and a motor brake with the same.
2. Description of the Related Art
A greater number of brakes that employ a motor as a power source have recently been equipped in vehicles. A representative example is a disc type motor brake that employs a motor as a power source of a drive device adapted to press a frictional pad.
A disc type motor brake includes a disc to rotate along with a vehicle wheel, a pair of friction pads to press the disc, a carrier to support the pair of frictional pads, a piston to press any one of the pair of frictional pads against the disc, a caliper housing including a cylinder in which a piston is accommodated, the caliper housing being reciprocally movably supported by the carrier, a motor to generate forward/reverse rotation force, and a conversion unit to convert rotation of a motor into rectilinear reciprocation of the piston, the conversion unit generally adopting a screw-shaft coupled to the piston.
In the above-described motor brake, drive power of the motor is transmitted to the screw-shaft constituting the conversion unit, and the piston, rotation of which is limited based on a rotating direction of the screw-shaft, rectilinearly reciprocates to press one frictional pad against the disc, realizing braking.
In general, a decelerator is typically used to increase torque because of high revolutions per minute (RPM) and low torque of the motor. In the above-described motor brake, a decelerator to increase drive power of the motor is connected between the motor and the conversion unit.
To achieve an enhanced deceleration ratio, the decelerator is typically configured such that a plurality of planet gear units is stacked one above another in an axial direction of the motor to realize multi-stage deceleration.
However, in the case of the decelerator having the plurality of planet gear units stacked in the axial direction of the motor, the overall length of the brake formed in the axial direction of the motor is excessively increased, which causes deterioration in space utility of a vehicle.